Much research and testing has been accomplished to help alleviate the rider problems associated with more than one rider riding the same two-wheeled vehicle, commonly known as a tandem bicycle. There are in use two person, three person, and four person tandem bicycles. As conventionally built, the pedal sets for each rider drive a common drive line, commonly a chain, at the same speed. Thus, although there may be provision for gear ratio change at the rear wheel, the multiple pedal sets of the multiple riders are mechanically linked together at all times and must rotate at the same relative spinning rpm rate in lock-step.
The problems with current drive line systems for tandem bicycles have been the same since the origins of tandem bicycles. The requirements for each rider to match his optimum pedal spinning rpm rate, the amounts of torque each rider puts into the drive line, the inability of one rider to ride differently than the other(s) and how each rider rests certain muscle groups during the ride have always been a compromise at best.